CA1255398A - Apparatus for measuring the thickness profile of rolled strips - Google Patents
Apparatus for measuring the thickness profile of rolled stripsInfo
- Publication number
- CA1255398A CA1255398A CA000515114A CA515114A CA1255398A CA 1255398 A CA1255398 A CA 1255398A CA 000515114 A CA000515114 A CA 000515114A CA 515114 A CA515114 A CA 515114A CA 1255398 A CA1255398 A CA 1255398A
- Authority
- CA
- Canada
- Prior art keywords
- radiation
- slit diaphragm
- rotation
- measuring
- slit
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B15/00—Measuring arrangements characterised by the use of electromagnetic waves or particle radiation, e.g. by the use of microwaves, X-rays, gamma rays or electrons
- G01B15/02—Measuring arrangements characterised by the use of electromagnetic waves or particle radiation, e.g. by the use of microwaves, X-rays, gamma rays or electrons for measuring thickness
- G01B15/025—Measuring arrangements characterised by the use of electromagnetic waves or particle radiation, e.g. by the use of microwaves, X-rays, gamma rays or electrons for measuring thickness by measuring absorption
Abstract
Abstract To determine the thickness profile of rolled metal sheets by measuring the absorption of X-rays a slit diaphragm is used which is rotatable about the imaginary centre axis of the X-ray tube, the rotation consisting of a reciprocating movement lying in a range of less than 36°. Between the reversal points of the rotation the rotational movement takes place in steps with rest intervals lying therebetween.
(Fig. 1)
(Fig. 1)
Description
~25~i39~3 `
The invention relates to an apparatus for measuring the thickness profile of rolled metal sheets and sheet strips comprising an X-ray tube, a movable slit diaphragm lying closely in front of said tube and radiation receivers which are spaced in front of said diaphragm and fixedly installed along a line and aligned with the radiation, the sheet or sheet strip to be measured being moved through the radiation between the X-ray tube or slit diaphragm and the radiation receivers in such a manner that its width extends along the line of the fixedly inst~lled radiation receivers, and con-nected to the radiation receivers and a displacement sensor of the slit position is a processing unit for determining the radiation absorption and the association with the thick-nesses of the sheet strip and the measuring points or measur-ing regions distributed over the width of the sheet strip, said unit being connected to a display device.
An apparatus for thickness profile measurement is known from German patent application 3,140,714, published ,, ~
April 28, 1983 in the names of Flormann et al. This appara-tus has the disadvantage that only relatively inaccurate measur-ments can be carried out. Due to the size of the receivers it is not possible to divide the sheet metal strip to be measured into narrow regions between which no regions which are not mea,sured lie. A further disadvantage is that the number of radiation receivers used is very high and this makes the apparatus complicated~and expensive.
U. S. patent 3,866,047 discloses a further apparatus whlch overcomes these disadvantages by operating with wide radi-atlon receivers and a~ moving slit diaphragm.
- ,.
~:255398 This construction has the disadvantage that no narrow measuring regions can be achieved bacause they would require very narrow slits in the slit diaphragm. The linear movement of the slit diaphragm in conjunction with narrow slits would mean that in the vicinity of the reversal points of the movement no radiation would pass through the slits.
The centre axis of the slit would coincide with the beam direction, enabling the full radiation to pass through the slit, only exactly in the centre of the movement of the slit diaphragm. This error can be eliminated adequately only if the slit diaphragm has a relatively large distance from the radiation source, is made relatively long and with relatively wide slits. Such-`a slit diaphragm has a large mass and for that reason persecond only a few measured values can be determined because the slit diaphragm can be oscillated only very slowly. This large mass also causes vibratory motions of the entire frame and as a result in particular with rela-tively large distances between the radiation source and the radiation receiver narrow measuring ranges are not possible.
GB patent 2,084,829 also discloses a rotating slit diaphragm ~ .
which does not cause any vibrations. With this slit diaphragm ::
the distance between the radiation source and the slit diaphragm ~ must once again be relatlvely large and this also leads to in-;~ ;adequate~local resolutlon.
A rotating slit diaphragm lying closely in front of the radiation source and having extremely narrow slits is des-cribed in German patent application P 34 25 295 published ' !
~ February 12, 1986 in the name of Huesch A.~.... In this case, '.'.'~, I`, pg~
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due to the rotation movement of the slit diaphragm led round the radiation source the centre axis of each slit always coin-cides with the beam direction. The apparatus according to P 34 25 ~95 thus has the necessary high local resolution necessary for use in rolling mills. A disadvantage resides in the large number of slits of which only about one tenth is used and traversed at any instant. The extremely accurate pro-duction of the narrow slits is very expensive. A further disadvan-,~
- tage resides in that small errors are inevitable in the slit pro-~10 duction. With the large distances to the radiation receivers small e~rrors manifest themselves to such an extent that they have :i:' ' , to be taken into account in the evaluation by a correction factor.
In the practical construction 150 slits of about 1 mm ~- width are necessary for the slit diaphragm and the series of radiation receivers includes 14 radiation receivers so that 150 times 14 correction factors arise and taking these into account involves a great deal of computing expenditure in the processing ~- unit. A further disadvantage resides in that with the rough .;
rolling milling conditions and the necessary extremely accurate ~20 measurements the apparatus must be recalibrated very frequently and then each correction factor must be redetermined.
The present invention is based on the problem of ` providing an apparatus for measuring the thickness profile of .: :
rolled metal strips which whilst retaining a high local re-,, .
solution of the measurements makes do with a slit diaphragm ~;~ which is easy to make and a small processing unit which is easy to calibrate and in which moreover the measurement results are . :
~ ~ measured at an exact constant distance from the edge of the , .~
strip. ~ ~
,:;
~2~53~3 Specifically, the invention relates to an apparatus for measuring the thickness profile of rolled metal sheets and sheet strips comprising an X-ray tube, a movable slit diaphragm lying closely in front of the tube and radiation receivers which are spaced in front of the diaphragm and fixedlY installed along a line and aligned with the radiation. The sheet or sheet strip to be measured moves through the radiation between the X-ray tube or slit diaphragm and the radiation receivers in such a manner that its width extends along the line of the radiation receivers. A processing unlt is connected to the radiation receivers and to a displacement sensor for slit position for determining the radiation absorption and the association with the thicknesses of the sheet strip and the measuring points or measuring regions distributed over the width of the sheet strip. The processing unit is connected to a display deviceO The slit diaphragm is rotatable about the centre axis of the X-ray tube and is connected to a drive which reverses the direction of ro.tation of the slit diaphragm after less than every one tenth of a revolution.
~, 20 The slit diaphragm need only be reciprocated through ,, .
the extremely small rotation of less that 5 because it is -~~ : mounted as close as possible to the X-ray tube and at the same . time the radiation:receivers are disposed relatively remotely from the X-ray tube and the slit diaphragm is provided with a rela-tively large number of slits.
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$:25~398 The overall length of the slit diaphragm, due to the close-ness to the X-ray tube, is relatively short and its mass is thus small. Due to the small rotation of less than 5 only a relatively small angular velocity is required. As a result only small forces of inertia occur at the reversal points of the movemen-t. The small forces of inertia can be taken up by the support means of the apparatus without any mass balancing whatever without disturbing vibrations ma]c-ing themselves felt. It is of course also possible to pro-vide a mass compensation in the form of a mass which is moved opposite to the direction of rotation of the slit diaphragm and the movement of which is derived by a gear reversing the dixection of rotation for example from the movement of the slit diaphragm.
The magnitude of the rotation movement may be still further reduced if the number of slits in the slit diaphragm is in-creased. It is expedient for a slit to be provided in the slit diaphragm for each radiation receiver. The rotation range of a slit may also extend over two or more radiation recelvers.
The thickness of narrow strips of the metal strip lying exactly in the strip travelling direction is measured if the rotation of the slit diaphraym takes place in steps with intermedia-te residence times in which the slit diaphragm is stationary and the measured value pickup of the processing unit is switched on during the residence time between two steps of the slit diaphragm.
The switching on and off of the measured value pickup is by a~switch or a contactless-switching switching element which are attached to the drlve of the slit diaphragm, preferably on a shaft which rotates exactly one revolution per step of the slit diaphragm. The switch may for example be actuated by a suitably shaped cam mounted on the shaft or contactless by for example~reflected light beams in known manner.
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It is expedient for the rotation of the slit diaphragm to be only of a magnitude such that the beam sweeps over less than 95~ of -the effective length of the radiation receiver and at the edges of the radiation receiver narrow regions are omitted. These narrow regions serve as compensating reserve if during operation for example due to thermal ex-pansions small location differences occur between the slit diaphragm and the radiation receivers. In this manner it is ensured that the first and last measuring region always lie entirely on -the radiation receiver.
Another possibility of compensating small position differ-ences is obtained if the start of the first measuring region in the passage of a radiation receiver begins in the small intermediate space inoperative for radiation between the radiation receivers and the measured value of the first measuring region is taken into account by a corresponding correction factor for the radiation falling into the in-effective intermediate space. It is favourable for this correction factor to be redetermined as often as possible, for example af-ter every strip passage, by a calibrating measurement. It should however be redetermined at the latest every 2 hours. If the intermediate space is for example 6 mm wide position differences effecting a devia-tion of the beam up to 6 mm from the desired position can be compensated.
:
The slit diaphgram has the form of a small segment of a circular ring. It is fully sufficient for the slit dia-phragm to be restricted to the tenth of a circle and into the slit diaphragm at equal distances apart 15 narrow slits are formed which extend radially in the direction to the imaginary centre point of the circular ring. The imaginary centre axis of the X-ray tube represents the axis of rotation of the circular ring. The beam passing through a slit str;ikes the radiation receiver associated with said slit about 2 m distance away from the slit diaphragm; said . ,~ .
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receiver can have a length of about 15 cm. The receiprocat-ing movement of the beam takes place only over the 15 cm length of the radiation receiver. The adjacent beam of the adjacent slit scans the adjacent radiation receiver. The reciproca-ting rotational movement of the slit diaphragm is over an angle which is less than 3.
When the strip to be measured is disposed such that the edge of the strip lies within a measuring region this measuring region cannot be used for the thickness profile determination.
It is then advantageous if in the processing unit the meas-ured value evaluation is connected so that for the thick-ness profile determination the measured value lying at the start of the passage after the last measured value showing no absorption is suppressed and likewise the measured value which towards the end of the passage lies before the first value showing no absorption is also suppressed.
' ~
The calibration of the apparatus is carried out during the operation in the short pauses between strip pas~ages by mak-ing a measurement without a strip to be measured being lo-cated in the apparatus and calculating a mean value from the measured values of the radiation receivers and providing each individual measured value of a measuring region with a correction factor in such a manner that the product measured value times correction value gives the mean value and stor-ing the correction factors thus formed in the processing unit and employing them for processing the measured values obtained when a strip is -traversed by the radia*ion.
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An example of embodiment will be explained in detail with --~ the aid of Figures 1 to 4.
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In the Figures:
Fig. l shows the apparatus with the X-ray tube and the slit diaphragm and the radiation receivers and .::. , . , ~
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Fig. 2 shows a switch controlled by a cam and Fiq. 3 is a general view of the devices following the radiation receivers and .
Fig. 4 shows a slit diaphragm.
The X-ray tube 11 is annularly surrounded by the shield 12.
The shield 12 has a window 13 through which a beam 14 is sent in the direction towards the radiation receivers 15 -29. The radiation receivers 15 - 29 are arranged on a cir-cular line whose centre point coincides with -the centre 30 of the X ray tube. In front of the window 13 there is the sli-t diaphragm 31 which is reciprocated in both directions of rotation by less than 3 about the centre 30 of the X-ray tube 11.
Secured to the slit diaphragm 31 is a stirrup member 32 which is mounted at the points 70 to 73 by for example rollérs. The drive of the slit diaphgram 31 for the recipro-cating pivot movement is effected by the motor 33 which may for example be a three-phase motor. The speed of rotation of the motor 33 is reduced in the gearing 34 and the stepp-ing gearing 35 is driven with the reduced speed.
The stepping~gearing 35 divides the continuous rotary motlon into a stepwise rotary motion. Every rotation lasting 60 milliseconds is followed by~a stationary period of 70 milli-seconds. This is effected in known manner within the stepp-ing gearing by for example a suitably formed cam. The pen-dulum gearing 36 is driven by the stepping gearing 35. In said pendulum gearing the rotary motion is converted in a manner known per se to a pendulum motion which is trans-mitted via the lever 37, the rod 38 and the lever 39 con-nected to~the stirrup member 32 to the slit diaphragm 31.
By the pendulum gearing 36 a movement reversal is achieved after every 14 steps of the stepping gearing 35. The radiation :
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receivers 15 - 29 in one example of embodiment are 150 mm long and arranged on a circle beneath the strip 40 to be in-vestigated between two rollers of an exit roller table of a rolling mill, which is not shown, such that they all have the same distance from the centre point 30 of the X-ray tube 11.
The X-ray tube is arranged above the exit roller table.
The ratios in the gearings are matched so that the shaft 41 executes exactly one revolution whilst the slit diaphragm advances by one step and stops between the steps. A switch 43 is disposed above a cam 42 which is secured to the shaft 41. Said cam switches the switch 43 on for example during one half of the revolution and off during the other half.
Said switch 43 may be mechanically actuated but may also have contactless actuation for example with the aid of an interrupted light beam when for example the upper part of the cam in Fig. 2 interrupts the light beam of a light barrier and the lower part with lesser radius allows the light beam to pass, thus initiating the switching functions.
The switch 43 is set such that a switching takes place at every start and end of the rest intervals between the steps of the stepping gearing 35. This switching information of the switch 43 is passed via the line 44 to a displacement pickup.
The displacement pickup is connected to each of the radiation recelvers lS - 29 via in each~case an amplifier 68. The output of the displacement pickup 45 is connected to the processing unit 46 whose output is in turn connected to the dlsplay devi~e~69.;~
The~switch 43 effects by ~its slgnal passing v1a the displace-ment pickup 45 to the processing unit 46 that all measure-ment signals coming from the radiation receivers 15 to 29 ;during the movement of the slit diaphragm 31 are suppressed ,. ~`' "':' ' S3~
and only the measurement signals arriving in the rest inter-vals between the steps are processed.
The radiation receiver 15 illustrated in Fig. 3 comprises 14 measuring regions which are shown in dashed line and designated by 47 to 61. The first measuring regions of the radiation receiver 16 adjacent the former receiver are designated by 62 to 65 a.
In Fig. 3 the beam 66 allowed to pass by the slit diaphragm 31 is located in the measuring region 51 whilst the follow-ing slit of the slit diaphragm allows a beam 67 to pass onto the measuring region 65 a of the following radiation re-ceiver 16.
When the slit diaphragm 31 is turned by the motor 33 and the interposed gearings the beam 66 passes through the measuring regions from the radiation receiver 15 in the di-rection to the radiation receiver 16 and back again in 4 seconds. If the beam 66 for example is on the measuring ~region 51~during the interval between the steps the beam is weakened correspondin~g to the thickness of the strip 40 to be traversed. In the radiation receiver 15 a current depending on the intensity of the beam 66 is generated.
This current flows via the amplifier 68 to the displacement pickup 45 in the~processing unit 46 where it is processed to give a quantity corresponding to the thickness of the strip 40. Thls~measured quantlty is passed onto the display device. In addition to the display device other devices may also be connected, for example for correctiny the rolling process.
The~ switch 43~effects in ita for example interrupted posi-tion by i-ts connection~to the processing unit that~all measurement signals coming from the radiation receivers 15 29 are suppressed~when~for example during a half revolution of the shaft 41 the slit diaphragm 31 is advanced by one step.
g :: : . . : -: . . : .- : .-, . : :
~553~13 The measurement signals are not processed again until in the other half of the revolution of the shaft 41 the switch moves into the closed position.
In the displacement pickup 45 the number of current inter-ruptions of the switch 43 is counted. The amplifier 68 superimposes on the output current a recognition signal differing from the recognition signals of the other ampli-fiers which are connected after the other radiation receivers.
From the recognition signal the displacement pickup 45 recognises to which radiation receiver the quantity is to be assigned and from the counted number of interruptions of the switch 43 the displacement pickup recognlses in which measuring region of the respective radiation receiver the beam is located at that instant.
The displacement pickup 45 passes the measured quantity to-gether with a signal associated wlth each measuring region to the processing unit 46. The latter is essen-tially a programmed computer which in a manner known per se calcu-lates from the measured intensity of the received beam the thickness of the strip 40, also making corrections for dis-turbing influences. Account is taken and a correction made ~; ;for example~for the f`act that the intensity distribution of ; the X-ray tube is not uniform over the width of the radiation window. A correction can also be ma~de for the varying sensitivity over the width of the radiation receiver. The values of the individual measuring regions can be supplied to a display device 69 whose screen is also divided into an equal number of measuring regions. A narrow strip on the screen of the display device 69 corresponds in analog manner and in position to each of the measuring regions 47 to 61. These strips are indicated in dashed line. The values of the thickness of the strip 40 may~be displayed digitally but~they may also be represented as dots on the screen, the vertical position of the dots corresponding to - ~
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~25S3~8 the magnitude of the thickness. The dots may also be con-nected to form a curve. Any other desired display device can also be connected.
In the displacement generating means or pickup 45 in the example of embodiment after every 14th step the counting for the assignment of the measuring regions is restarted~
Suitable radiation receivers are for example plastic scin-tillators which are followed in known manner by photomulti-pliers and amplifiers or counting means.
In the example given the distance from the centre 30 of the X-ray tube 11 to the radiation receivers 15 to 29 is 3820 mm.
The distance from the strip to the centre radiation re-ceiver is 1200 mm. The distance from the centre of the slit diaphragm 31 to the centre 30 of the X~ray tube 11 is 530 mm. The slit diaphragm 31 has a thickness in the beam direction of 180 mm. In the slit diaphragm 31;15 slits are disposed. Each slit is 1.2 mm wide and is spaced from the next slit a distance of about 21 mm. In the example given the two major boundary faces of the sli-ts ale plane-parallel.
A still greater accuracy would be achieved if these boundary faces were somewhat wedge-shaped with respect to each other correspondin~q~to the beam direction. The apparatus ls able to measure~thickness fluctuations of the strip down~to~less ;than 2 per mi~
An~exact strip edge determination is effected for example if in accordance with Fig. 3 the beam 66 first~meets the measuring region 47 of~ the radiation recelver 15~ In this position there is no~absorption. In~the next measuring~
reglon 48 partial absorption occurs. In~the measuriny~region 49 and the~followins measurin~regions full absorption~occurs.
If for ex~ample the~me:suring region 48 gives a me~asured ~
value~whose difference to the measured value of~the~measuring ;,, ~ : ~ , . ................... .. ; -.................. :
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~:~55;~S8 region 47 is for example 40% of the difference of the measured values of the measuring regions 47 and 49, the strip edge lies 40% of the width of the measuring region to the right from the measuring region 47. If the difference is for ex-amle 30% the distance is 30% of the width to the right.
This distance is counted from the right side of the measur-ing region 47 to the right in the direction towards the measuring region 49. The storing of the measured values, formation of the difference of the measured values and cal-culation of the resulting position of the strip edge is carrled out in a manner known per se in the processing unit 46, which includes a computer.
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~2S53~38 11 X-ray tube 12 Shield 13 Window 14 Beam 29 Radiation receivers Centre of the X-ray tube 31 Slit diaphragm 32 Stirrup member 33 Motor 34 Gearing Stepping gearing 36 Pendulum gearing 37 Lever 38 Rod .~
39 Lever , 40 Strip , 41 Shaft 42 Cam :~: 43 Switch i~ 44 Line Displacement pickup 46 Processing unit 47 to 61 Measuring regions 62 to 65 Measuring regions :66 Beam : : 67 Be:am : 68 Amplifier 69 Display device ~ :
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The invention relates to an apparatus for measuring the thickness profile of rolled metal sheets and sheet strips comprising an X-ray tube, a movable slit diaphragm lying closely in front of said tube and radiation receivers which are spaced in front of said diaphragm and fixedly installed along a line and aligned with the radiation, the sheet or sheet strip to be measured being moved through the radiation between the X-ray tube or slit diaphragm and the radiation receivers in such a manner that its width extends along the line of the fixedly inst~lled radiation receivers, and con-nected to the radiation receivers and a displacement sensor of the slit position is a processing unit for determining the radiation absorption and the association with the thick-nesses of the sheet strip and the measuring points or measur-ing regions distributed over the width of the sheet strip, said unit being connected to a display device.
An apparatus for thickness profile measurement is known from German patent application 3,140,714, published ,, ~
April 28, 1983 in the names of Flormann et al. This appara-tus has the disadvantage that only relatively inaccurate measur-ments can be carried out. Due to the size of the receivers it is not possible to divide the sheet metal strip to be measured into narrow regions between which no regions which are not mea,sured lie. A further disadvantage is that the number of radiation receivers used is very high and this makes the apparatus complicated~and expensive.
U. S. patent 3,866,047 discloses a further apparatus whlch overcomes these disadvantages by operating with wide radi-atlon receivers and a~ moving slit diaphragm.
- ,.
~:255398 This construction has the disadvantage that no narrow measuring regions can be achieved bacause they would require very narrow slits in the slit diaphragm. The linear movement of the slit diaphragm in conjunction with narrow slits would mean that in the vicinity of the reversal points of the movement no radiation would pass through the slits.
The centre axis of the slit would coincide with the beam direction, enabling the full radiation to pass through the slit, only exactly in the centre of the movement of the slit diaphragm. This error can be eliminated adequately only if the slit diaphragm has a relatively large distance from the radiation source, is made relatively long and with relatively wide slits. Such-`a slit diaphragm has a large mass and for that reason persecond only a few measured values can be determined because the slit diaphragm can be oscillated only very slowly. This large mass also causes vibratory motions of the entire frame and as a result in particular with rela-tively large distances between the radiation source and the radiation receiver narrow measuring ranges are not possible.
GB patent 2,084,829 also discloses a rotating slit diaphragm ~ .
which does not cause any vibrations. With this slit diaphragm ::
the distance between the radiation source and the slit diaphragm ~ must once again be relatlvely large and this also leads to in-;~ ;adequate~local resolutlon.
A rotating slit diaphragm lying closely in front of the radiation source and having extremely narrow slits is des-cribed in German patent application P 34 25 295 published ' !
~ February 12, 1986 in the name of Huesch A.~.... In this case, '.'.'~, I`, pg~
. .
::
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'. ~ , ' ' , ' .~`. '' ' ' . ` `
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due to the rotation movement of the slit diaphragm led round the radiation source the centre axis of each slit always coin-cides with the beam direction. The apparatus according to P 34 25 ~95 thus has the necessary high local resolution necessary for use in rolling mills. A disadvantage resides in the large number of slits of which only about one tenth is used and traversed at any instant. The extremely accurate pro-duction of the narrow slits is very expensive. A further disadvan-,~
- tage resides in that small errors are inevitable in the slit pro-~10 duction. With the large distances to the radiation receivers small e~rrors manifest themselves to such an extent that they have :i:' ' , to be taken into account in the evaluation by a correction factor.
In the practical construction 150 slits of about 1 mm ~- width are necessary for the slit diaphragm and the series of radiation receivers includes 14 radiation receivers so that 150 times 14 correction factors arise and taking these into account involves a great deal of computing expenditure in the processing ~- unit. A further disadvantage resides in that with the rough .;
rolling milling conditions and the necessary extremely accurate ~20 measurements the apparatus must be recalibrated very frequently and then each correction factor must be redetermined.
The present invention is based on the problem of ` providing an apparatus for measuring the thickness profile of .: :
rolled metal strips which whilst retaining a high local re-,, .
solution of the measurements makes do with a slit diaphragm ~;~ which is easy to make and a small processing unit which is easy to calibrate and in which moreover the measurement results are . :
~ ~ measured at an exact constant distance from the edge of the , .~
strip. ~ ~
,:;
~2~53~3 Specifically, the invention relates to an apparatus for measuring the thickness profile of rolled metal sheets and sheet strips comprising an X-ray tube, a movable slit diaphragm lying closely in front of the tube and radiation receivers which are spaced in front of the diaphragm and fixedlY installed along a line and aligned with the radiation. The sheet or sheet strip to be measured moves through the radiation between the X-ray tube or slit diaphragm and the radiation receivers in such a manner that its width extends along the line of the radiation receivers. A processing unlt is connected to the radiation receivers and to a displacement sensor for slit position for determining the radiation absorption and the association with the thicknesses of the sheet strip and the measuring points or measuring regions distributed over the width of the sheet strip. The processing unit is connected to a display deviceO The slit diaphragm is rotatable about the centre axis of the X-ray tube and is connected to a drive which reverses the direction of ro.tation of the slit diaphragm after less than every one tenth of a revolution.
~, 20 The slit diaphragm need only be reciprocated through ,, .
the extremely small rotation of less that 5 because it is -~~ : mounted as close as possible to the X-ray tube and at the same . time the radiation:receivers are disposed relatively remotely from the X-ray tube and the slit diaphragm is provided with a rela-tively large number of slits.
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$:25~398 The overall length of the slit diaphragm, due to the close-ness to the X-ray tube, is relatively short and its mass is thus small. Due to the small rotation of less than 5 only a relatively small angular velocity is required. As a result only small forces of inertia occur at the reversal points of the movemen-t. The small forces of inertia can be taken up by the support means of the apparatus without any mass balancing whatever without disturbing vibrations ma]c-ing themselves felt. It is of course also possible to pro-vide a mass compensation in the form of a mass which is moved opposite to the direction of rotation of the slit diaphragm and the movement of which is derived by a gear reversing the dixection of rotation for example from the movement of the slit diaphragm.
The magnitude of the rotation movement may be still further reduced if the number of slits in the slit diaphragm is in-creased. It is expedient for a slit to be provided in the slit diaphragm for each radiation receiver. The rotation range of a slit may also extend over two or more radiation recelvers.
The thickness of narrow strips of the metal strip lying exactly in the strip travelling direction is measured if the rotation of the slit diaphraym takes place in steps with intermedia-te residence times in which the slit diaphragm is stationary and the measured value pickup of the processing unit is switched on during the residence time between two steps of the slit diaphragm.
The switching on and off of the measured value pickup is by a~switch or a contactless-switching switching element which are attached to the drlve of the slit diaphragm, preferably on a shaft which rotates exactly one revolution per step of the slit diaphragm. The switch may for example be actuated by a suitably shaped cam mounted on the shaft or contactless by for example~reflected light beams in known manner.
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It is expedient for the rotation of the slit diaphragm to be only of a magnitude such that the beam sweeps over less than 95~ of -the effective length of the radiation receiver and at the edges of the radiation receiver narrow regions are omitted. These narrow regions serve as compensating reserve if during operation for example due to thermal ex-pansions small location differences occur between the slit diaphragm and the radiation receivers. In this manner it is ensured that the first and last measuring region always lie entirely on -the radiation receiver.
Another possibility of compensating small position differ-ences is obtained if the start of the first measuring region in the passage of a radiation receiver begins in the small intermediate space inoperative for radiation between the radiation receivers and the measured value of the first measuring region is taken into account by a corresponding correction factor for the radiation falling into the in-effective intermediate space. It is favourable for this correction factor to be redetermined as often as possible, for example af-ter every strip passage, by a calibrating measurement. It should however be redetermined at the latest every 2 hours. If the intermediate space is for example 6 mm wide position differences effecting a devia-tion of the beam up to 6 mm from the desired position can be compensated.
:
The slit diaphgram has the form of a small segment of a circular ring. It is fully sufficient for the slit dia-phragm to be restricted to the tenth of a circle and into the slit diaphragm at equal distances apart 15 narrow slits are formed which extend radially in the direction to the imaginary centre point of the circular ring. The imaginary centre axis of the X-ray tube represents the axis of rotation of the circular ring. The beam passing through a slit str;ikes the radiation receiver associated with said slit about 2 m distance away from the slit diaphragm; said . ,~ .
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receiver can have a length of about 15 cm. The receiprocat-ing movement of the beam takes place only over the 15 cm length of the radiation receiver. The adjacent beam of the adjacent slit scans the adjacent radiation receiver. The reciproca-ting rotational movement of the slit diaphragm is over an angle which is less than 3.
When the strip to be measured is disposed such that the edge of the strip lies within a measuring region this measuring region cannot be used for the thickness profile determination.
It is then advantageous if in the processing unit the meas-ured value evaluation is connected so that for the thick-ness profile determination the measured value lying at the start of the passage after the last measured value showing no absorption is suppressed and likewise the measured value which towards the end of the passage lies before the first value showing no absorption is also suppressed.
' ~
The calibration of the apparatus is carried out during the operation in the short pauses between strip pas~ages by mak-ing a measurement without a strip to be measured being lo-cated in the apparatus and calculating a mean value from the measured values of the radiation receivers and providing each individual measured value of a measuring region with a correction factor in such a manner that the product measured value times correction value gives the mean value and stor-ing the correction factors thus formed in the processing unit and employing them for processing the measured values obtained when a strip is -traversed by the radia*ion.
:: :
An example of embodiment will be explained in detail with --~ the aid of Figures 1 to 4.
`~;:
In the Figures:
Fig. l shows the apparatus with the X-ray tube and the slit diaphragm and the radiation receivers and .::. , . , ~
,, , . . -.
' , ~ ' : :' ' ,: ` ::
~ ' ., ,.~.. . .
- -: , .
ii53~
Fig. 2 shows a switch controlled by a cam and Fiq. 3 is a general view of the devices following the radiation receivers and .
Fig. 4 shows a slit diaphragm.
The X-ray tube 11 is annularly surrounded by the shield 12.
The shield 12 has a window 13 through which a beam 14 is sent in the direction towards the radiation receivers 15 -29. The radiation receivers 15 - 29 are arranged on a cir-cular line whose centre point coincides with -the centre 30 of the X ray tube. In front of the window 13 there is the sli-t diaphragm 31 which is reciprocated in both directions of rotation by less than 3 about the centre 30 of the X-ray tube 11.
Secured to the slit diaphragm 31 is a stirrup member 32 which is mounted at the points 70 to 73 by for example rollérs. The drive of the slit diaphgram 31 for the recipro-cating pivot movement is effected by the motor 33 which may for example be a three-phase motor. The speed of rotation of the motor 33 is reduced in the gearing 34 and the stepp-ing gearing 35 is driven with the reduced speed.
The stepping~gearing 35 divides the continuous rotary motlon into a stepwise rotary motion. Every rotation lasting 60 milliseconds is followed by~a stationary period of 70 milli-seconds. This is effected in known manner within the stepp-ing gearing by for example a suitably formed cam. The pen-dulum gearing 36 is driven by the stepping gearing 35. In said pendulum gearing the rotary motion is converted in a manner known per se to a pendulum motion which is trans-mitted via the lever 37, the rod 38 and the lever 39 con-nected to~the stirrup member 32 to the slit diaphragm 31.
By the pendulum gearing 36 a movement reversal is achieved after every 14 steps of the stepping gearing 35. The radiation :
, . : .::, :
: :: :: : : ~ : : :
~L25S3g~
receivers 15 - 29 in one example of embodiment are 150 mm long and arranged on a circle beneath the strip 40 to be in-vestigated between two rollers of an exit roller table of a rolling mill, which is not shown, such that they all have the same distance from the centre point 30 of the X-ray tube 11.
The X-ray tube is arranged above the exit roller table.
The ratios in the gearings are matched so that the shaft 41 executes exactly one revolution whilst the slit diaphragm advances by one step and stops between the steps. A switch 43 is disposed above a cam 42 which is secured to the shaft 41. Said cam switches the switch 43 on for example during one half of the revolution and off during the other half.
Said switch 43 may be mechanically actuated but may also have contactless actuation for example with the aid of an interrupted light beam when for example the upper part of the cam in Fig. 2 interrupts the light beam of a light barrier and the lower part with lesser radius allows the light beam to pass, thus initiating the switching functions.
The switch 43 is set such that a switching takes place at every start and end of the rest intervals between the steps of the stepping gearing 35. This switching information of the switch 43 is passed via the line 44 to a displacement pickup.
The displacement pickup is connected to each of the radiation recelvers lS - 29 via in each~case an amplifier 68. The output of the displacement pickup 45 is connected to the processing unit 46 whose output is in turn connected to the dlsplay devi~e~69.;~
The~switch 43 effects by ~its slgnal passing v1a the displace-ment pickup 45 to the processing unit 46 that all measure-ment signals coming from the radiation receivers 15 to 29 ;during the movement of the slit diaphragm 31 are suppressed ,. ~`' "':' ' S3~
and only the measurement signals arriving in the rest inter-vals between the steps are processed.
The radiation receiver 15 illustrated in Fig. 3 comprises 14 measuring regions which are shown in dashed line and designated by 47 to 61. The first measuring regions of the radiation receiver 16 adjacent the former receiver are designated by 62 to 65 a.
In Fig. 3 the beam 66 allowed to pass by the slit diaphragm 31 is located in the measuring region 51 whilst the follow-ing slit of the slit diaphragm allows a beam 67 to pass onto the measuring region 65 a of the following radiation re-ceiver 16.
When the slit diaphragm 31 is turned by the motor 33 and the interposed gearings the beam 66 passes through the measuring regions from the radiation receiver 15 in the di-rection to the radiation receiver 16 and back again in 4 seconds. If the beam 66 for example is on the measuring ~region 51~during the interval between the steps the beam is weakened correspondin~g to the thickness of the strip 40 to be traversed. In the radiation receiver 15 a current depending on the intensity of the beam 66 is generated.
This current flows via the amplifier 68 to the displacement pickup 45 in the~processing unit 46 where it is processed to give a quantity corresponding to the thickness of the strip 40. Thls~measured quantlty is passed onto the display device. In addition to the display device other devices may also be connected, for example for correctiny the rolling process.
The~ switch 43~effects in ita for example interrupted posi-tion by i-ts connection~to the processing unit that~all measurement signals coming from the radiation receivers 15 29 are suppressed~when~for example during a half revolution of the shaft 41 the slit diaphragm 31 is advanced by one step.
g :: : . . : -: . . : .- : .-, . : :
~553~13 The measurement signals are not processed again until in the other half of the revolution of the shaft 41 the switch moves into the closed position.
In the displacement pickup 45 the number of current inter-ruptions of the switch 43 is counted. The amplifier 68 superimposes on the output current a recognition signal differing from the recognition signals of the other ampli-fiers which are connected after the other radiation receivers.
From the recognition signal the displacement pickup 45 recognises to which radiation receiver the quantity is to be assigned and from the counted number of interruptions of the switch 43 the displacement pickup recognlses in which measuring region of the respective radiation receiver the beam is located at that instant.
The displacement pickup 45 passes the measured quantity to-gether with a signal associated wlth each measuring region to the processing unit 46. The latter is essen-tially a programmed computer which in a manner known per se calcu-lates from the measured intensity of the received beam the thickness of the strip 40, also making corrections for dis-turbing influences. Account is taken and a correction made ~; ;for example~for the f`act that the intensity distribution of ; the X-ray tube is not uniform over the width of the radiation window. A correction can also be ma~de for the varying sensitivity over the width of the radiation receiver. The values of the individual measuring regions can be supplied to a display device 69 whose screen is also divided into an equal number of measuring regions. A narrow strip on the screen of the display device 69 corresponds in analog manner and in position to each of the measuring regions 47 to 61. These strips are indicated in dashed line. The values of the thickness of the strip 40 may~be displayed digitally but~they may also be represented as dots on the screen, the vertical position of the dots corresponding to - ~
~,; , . -:: :, - :; . :
,~ :, , , : : :: :
~25S3~8 the magnitude of the thickness. The dots may also be con-nected to form a curve. Any other desired display device can also be connected.
In the displacement generating means or pickup 45 in the example of embodiment after every 14th step the counting for the assignment of the measuring regions is restarted~
Suitable radiation receivers are for example plastic scin-tillators which are followed in known manner by photomulti-pliers and amplifiers or counting means.
In the example given the distance from the centre 30 of the X-ray tube 11 to the radiation receivers 15 to 29 is 3820 mm.
The distance from the strip to the centre radiation re-ceiver is 1200 mm. The distance from the centre of the slit diaphragm 31 to the centre 30 of the X~ray tube 11 is 530 mm. The slit diaphragm 31 has a thickness in the beam direction of 180 mm. In the slit diaphragm 31;15 slits are disposed. Each slit is 1.2 mm wide and is spaced from the next slit a distance of about 21 mm. In the example given the two major boundary faces of the sli-ts ale plane-parallel.
A still greater accuracy would be achieved if these boundary faces were somewhat wedge-shaped with respect to each other correspondin~q~to the beam direction. The apparatus ls able to measure~thickness fluctuations of the strip down~to~less ;than 2 per mi~
An~exact strip edge determination is effected for example if in accordance with Fig. 3 the beam 66 first~meets the measuring region 47 of~ the radiation recelver 15~ In this position there is no~absorption. In~the next measuring~
reglon 48 partial absorption occurs. In~the measuriny~region 49 and the~followins measurin~regions full absorption~occurs.
If for ex~ample the~me:suring region 48 gives a me~asured ~
value~whose difference to the measured value of~the~measuring ;,, ~ : ~ , . ................... .. ; -.................. :
. ~ -, . , : . --::
: .
~:~55;~S8 region 47 is for example 40% of the difference of the measured values of the measuring regions 47 and 49, the strip edge lies 40% of the width of the measuring region to the right from the measuring region 47. If the difference is for ex-amle 30% the distance is 30% of the width to the right.
This distance is counted from the right side of the measur-ing region 47 to the right in the direction towards the measuring region 49. The storing of the measured values, formation of the difference of the measured values and cal-culation of the resulting position of the strip edge is carrled out in a manner known per se in the processing unit 46, which includes a computer.
:, ~
~2S53~38 11 X-ray tube 12 Shield 13 Window 14 Beam 29 Radiation receivers Centre of the X-ray tube 31 Slit diaphragm 32 Stirrup member 33 Motor 34 Gearing Stepping gearing 36 Pendulum gearing 37 Lever 38 Rod .~
39 Lever , 40 Strip , 41 Shaft 42 Cam :~: 43 Switch i~ 44 Line Displacement pickup 46 Processing unit 47 to 61 Measuring regions 62 to 65 Measuring regions :66 Beam : : 67 Be:am : 68 Amplifier 69 Display device ~ :
, : . ~ ., .:. ;, ~, .. , ,. : , : -; ~ . ~ . , . " ,
Claims (16)
1. Apparatus for measuring the thickness profile of rolled metal sheets and sheet strips (40) comprising an X-ray tube (11), a movable slit diaphragm (31) lying closely in front of said tube and radiation receivers (15 - 29) which are spaced in front of said diaphragm and fixedly installed along a line and aligned with the radiation, the sheet or sheet strip (40) to be measured being moved through the radiation between the X-ray tube (11) or slit diaphragm (31) and the radiation receivers (15 -29) in such a manner that its width extends along the line of the fixedly installed radiation receivers (15 -29), and connected to the radiation receivers and a displacement sensor (45) of the slit position is a pro-cessing unit (46) for determining the radiation absorp-tion and the association with the thicknesses of the sheet strip (40) and the measuring points or measuring regions (47) distributed over the width of the sheet strip (40), said unit (46) being connected to a display device (69), characterized in that the slit diaphragm (31) rotatable about the centre axis of the X-ray tube (11) is connected to a drive (36) which reverses the direction of rotation of the slit diaphragm (31) after less than every one tenth of a revolution.
2. Apparatus according to claim 1, characterized in that the number of slits corresponds to the number of radia-tion receivers (15 - 29) and each radiation receiver (15 - 29) is swept over in its entire length or at least 90% of the entire length by one of the beams (66) pass-ing through the slits in the entire partial rotation amounting to less than one tenth of a revolution.
3. Apparatus according to claim 1, characterized in that the partial rotation takes place in steps with intermediate residence times in which the slit diaphragm (31) is station-ary.
4. Apparatus according to claims 1 to 3, characterized in that the drive consists of a drive motor (33) with reduction gearing (34), a stepping gearing (35) attached thereto and a pendulum gearing (36) connected to the drive shaft thereof.
5. Apparatus according to claim 1, characterized in that attached to the drive is a mechanical switch (43) or a contactless-switching switching element which are adapted to be switched on and off by the rotation of a shaft (41) of the drive (34) and are connected to a displacement sensor (45) and a member of the processing unit (46) switching the measured value pickup on and off.
6. Apparatus according to claim 5, characterized in that the shaft (41) controlling the switching function for the switch (43) is designed as regards speed of rotation so that every step with residence time of the slit dia-phragm (31) corresponds exactly to one revolution of said shaft (41).
7. Apparatus according to claims 1 to 3, characterized in that the measured value pickup of the processing unit (46) is switched on during the residence time between two steps of the slit diaphragm (31).
8. Apparatus according to claims 1 to 3, characterized in that the displacement sensor (45) is connected to each individual radiation receiver (15 - 29) and to a step counter disposed in the processing (46).
9. Apparatus according to claims 1 to 3, characterized in that in the processing unit (46) the measuring ranges are determined whose adjacent measuring ranges on one side have no absorption and whose measuring ranges lying on the other side have a degree of absorption more than 2% higher and said measuring ranges thus determined with only partial absorption are suppressed in the display of the thickness profile and from the degree of the partial absorption and the position of the measuring range determined the exact position of the strip edge on the strip rolling train is determined and displayed.
10. Apparatus according to claims 1 to 3, characterized in that the partial rotation of the slit diaphragm (31) is dimensioned such that the beam (66) passing through the associated slit in the calibration in the desired state sweeps over less than 95% of the entire effective length of the radiation receiver (15), regions being omitted at both edges.
11. Apparatus according to claims 1 to 3, characterized in that the slit diaphragm (31) includes more than 6 slits and is connected to a gearing continuously reversing the direction of rotation and the maximum rotation angle between the reversal points is less than 8° and the distance from the centre of the slit diaphragm to the imaginary axis of rotation is less than 1/3 of the distance from the centre radiation receiver to the imaginary rotation axis of the slit diaphragm.
12. Apparatus according to claims 1 to 3, characterized in that the speed of rotation is chosen such that the rotational angle covered between the reversal points is covered in 0.5 to 4 sec.
13. Apparatus according to claims 1 to 3, characterized in that the radiation receivers are arranged along a circularly curved line whose centre point coincides with the imaginary rotation axis of the slit diaphragm (31).
14. Apparatus according to claims 1 to 3, characterized in that in the processing unit (46) the measured value evaluation is connected such that for the thickness profile indication the measured value which lies at the start of the passage after the last measured value which shows no absorption is suppressed and the measured value which towards the end of the passage lies before the first measured value which shows no absorption is also suppressed.
15. Apparatus according to claims 1 to 3, characterized in that the start of the measuring range falls into the edge range of the radiation receiver inoperative for reception and the radiation falling into said inoperative edge range is taken into account by a correction factor in the pro-cessing unit (46) and the correction factor is determined within periods of less than 2 hours by a calibration of the apparatus.
16. Method for calibrating the apparatus according to claims 1 to 3, characterized in that measurement is carried out without a strip (40) to be measured in the apparatus and a mean value calculated from the measured values of the radiation receivers (15 - 29) and each individual measured value of a measuring range (47) is provided with a correction factor in such a manner that the pro-duct measured value times correction factor gives the mean value and the correction values thus formed are stored in the processing unit (46) and used for the pro-cessing of the measured values obtained with a strip (40) traversed by the radiation.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3530109.0 | 1985-08-23 | ||
| DE19853530109 DE3530109A1 (en) | 1985-08-23 | 1985-08-23 | DEVICE FOR MEASURING THE THICKNESS PROFILE OF ROLLED TAPES |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1255398A true CA1255398A (en) | 1989-06-06 |
Family
ID=6279154
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000515114A Expired CA1255398A (en) | 1985-08-23 | 1986-07-31 | Apparatus for measuring the thickness profile of rolled strips |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4759046A (en) |
| EP (1) | EP0212078B1 (en) |
| JP (1) | JPH0739951B2 (en) |
| AT (1) | ATE58789T1 (en) |
| CA (1) | CA1255398A (en) |
| DE (2) | DE3530109A1 (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4928257A (en) * | 1988-01-25 | 1990-05-22 | Bethlehem Steel Corporation | Method and apparatus for monitoring the thickness profile of a strip |
| DE19722482A1 (en) * | 1997-05-28 | 1998-12-03 | Siemens Ag | Material testing plant |
| GB2355071A (en) * | 1999-10-08 | 2001-04-11 | Cintex Ltd | Non-contact volume measurement |
| DE19950254C2 (en) | 1999-10-18 | 2003-06-26 | Ims Messsysteme Gmbh | Method for determining a thickness cross profile and the thickness longitudinal profile of a running material strip |
| US6347131B1 (en) | 1999-11-02 | 2002-02-12 | Cintex Limited | Non-contact volume measurement |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3866047A (en) * | 1968-08-23 | 1975-02-11 | Emi Ltd | Penetrating radiation examining apparatus having a scanning collimator |
| US3790799A (en) * | 1972-06-21 | 1974-02-05 | American Science & Eng Inc | Radiant energy imaging with rocking scanning |
| GB1552224A (en) * | 1975-05-10 | 1979-09-12 | Heath Gloucester Ltd | Strip profile gauge |
| US4132895A (en) * | 1976-08-28 | 1979-01-02 | Emi Limited | Radiography |
| US4342914A (en) * | 1980-09-29 | 1982-08-03 | American Science And Engineering, Inc. | Flying spot scanner having arbitrarily shaped field size |
| US4495635A (en) * | 1981-04-03 | 1985-01-22 | Analogic Corporation | Method and apparatus for profiling structural sections |
| NL8103058A (en) * | 1981-06-24 | 1983-01-17 | Philips Nv | METHOD FOR CALIBRATING A GAMMA CAMERA AND GAMMA CAMERA WITH A CALIBRATION DEVICE |
| DE3138939A1 (en) * | 1981-09-30 | 1983-04-14 | Siemens AG, 1000 Berlin und 8000 München | X-RAY EXAMINATION DEVICE |
| DE3140714A1 (en) * | 1981-10-14 | 1983-04-28 | Paul Ing.(Grad.) Flormann | Device for measuring the thickness of flat sections |
| DE3425295C2 (en) * | 1984-07-10 | 1986-07-24 | Hoesch Ag, 4600 Dortmund | Device for measuring the thickness profile of rolled sheet metal strips |
-
1985
- 1985-08-23 DE DE19853530109 patent/DE3530109A1/en active Granted
-
1986
- 1986-05-17 DE DE8686106795T patent/DE3675843D1/en not_active Expired - Fee Related
- 1986-05-17 AT AT86106795T patent/ATE58789T1/en active
- 1986-05-17 EP EP86106795A patent/EP0212078B1/en not_active Expired - Lifetime
- 1986-07-31 CA CA000515114A patent/CA1255398A/en not_active Expired
- 1986-08-20 US US06/898,202 patent/US4759046A/en not_active Expired - Fee Related
- 1986-08-22 JP JP61195721A patent/JPH0739951B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| EP0212078A1 (en) | 1987-03-04 |
| DE3675843D1 (en) | 1991-01-10 |
| JPH0739951B2 (en) | 1995-05-01 |
| ATE58789T1 (en) | 1990-12-15 |
| JPS6247505A (en) | 1987-03-02 |
| DE3530109A1 (en) | 1987-03-05 |
| US4759046A (en) | 1988-07-19 |
| DE3530109C2 (en) | 1987-12-23 |
| EP0212078B1 (en) | 1990-11-28 |
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